Mechanically stabilized earth retaining walls are construction devices used to reinforce earthen slopes, particularly where changes in elevations occur rapidly. For example, parking lots and building sites have leveled subgrade or built-up above grade portions and typically with steeply rising embankments. These embankments must be secured, such as by retaining walls, against collapse or failure to protect persons and property from possible injury or damage caused by the slippage or sliding of the earthen slope.
Many designs for earth retaining walls exist today. Wall designs must account for lateral earth and water pressures, the weight of the wall, temperature and shrinkage effects, and earthquake loads. The design type known as mechanically stabilized earth retaining walls employ either metallic or polymeric tensile reinforcements in the soil mass. The tensile reinforcements extend laterally of the wall formed of a plurality of modular precast concrete members or blocks stacked together. The tensile reinforcements connect the soil mass to the blocks that define the wall. The blocks create a visual vertical facing for the reinforced soil mass.
The metallic tensile reinforcements typically used are non-extensible steel straps or meshes. The straps are either smooth or have transverse ribs. The meshes have longitudinal wires which connect to transversely aligned wires thereby forming a mesh like matrix. The modular precast concrete members may be in the form of blocks or panels that stack on top of each other to create the vertical facing of the wall.
The extruded polymeric tensile reinforcements typically used are-elongated lattice-like structures often referred to as grids. The grids have elongated ribs which connect to transversely aligned bars thereby forming elongated apertures between the ribs. Various connection methods are used to interlock the blocks or panels of the wall with the tensile reinforcements. One known type of retaining wall has precast concrete panels with steel yokes extending outwardly from the back side. The yokes receive nuts and bolts or pins. The edge portions of the tensile reinforcement straps or mesh are secured to the yokes by the bolts or pins. The straps or mesh extend laterally from the panels and are covered with backfill. The strength of the tensile reinforcement strap or mesh-to-wall connection is generated by the mechanical connection between the steel yoke and bolt or pin assembly to the tensile reinforcement strap or mesh. Another type of retaining wall has blocks with bores extending inwardly within the top and bottom surfaces. The bores receive dowels or pins. Edge portions of the polymeric tensile reinforcement grids or steel mesh are secured by the dowel pins. The tensile reinforcement extends laterally from the blocks and is covered with back fill. Subsequent tiers are constructed by placing blocks, with aggregate infill, in the wall. The strength of the tensile reinforcement grid or mesh-to-wall connection is generated by friction between the upper and lower block surfaces and the tensile reinforcement grid or mesh and the linkage between the aggregate trapped by the wall and the apertures of the tensile reinforcement grid or mesh. The magnitude of these two contributing factors varies with the workmanship of the wall, normal stresses applied by the weight of the wall above the connection, and by the quality and size of the aggregate.
Other connection devices are known. For example, my U.S. Pat. No. 5,417,523 describes a connector bar with spaced-apart keys that engage apertures in the tensile reinforcement grid that extends laterally from the wall. The connector bars are received in channels defined in the upper and lower surfaces of the blocks.
The specifications for earth retaining walls are based upon the strength of the interlocking components and the is load created by the backfill. Once the desired wall height and type of ground conditions are known, the strength of the tensile reinforcement, the number of tensile reinforcement, the vertical spacing between adjacent tensile reinforcement, and lateral positioning of the tensile reinforcement is determined, dependent upon the load capacity of the interlocking components.
Heretofore, construction of such mechanically stabilized earth retaining walls has been limited to the use of significantly expensive high strength tensile reinforcement. This is due in part to the efficiency of the tensile reinforcement-to-retaining wall connection. High strength steel straps and meshed are effectively non-extensible therefore they reach their peak tensile strength with a minimum of elongation and provide excellent tensile reinforcement-to-retaining wall connection. However, they are expensive and subject to corrosion. To reduce costs, tensile reinforcements other than steel straps or mesh have been developed for use with mechanically stabilized earth retaining walls. These other tensile reinforcements include extruded, woven, or knitted grids with large or small apertures, as well as woven or knitted textile sheets. These other tensile reinforcements are significantly less expensive than tensile reinforcement steel straps and mesh. However, they are extensible and therefore elongate 8 percent to 20 percent prior to reaching their peak tensile strength.
While these extruded, woven or knitted tensile reinforcement grids or sheets have been used to mechanically stabilize walls to backfill, there is a drawback. The lateral loading on the extending tensile reinforcement causes a portion of the tensile reinforcement to elongate and to move on a bearing surface of the block. The movement wears and abrades the tensile reinforcement, and leads to premature connection failure. To overcome this, designers generally “over-engineer” the strength of the tensile reinforcement. This leads to the use of tensile reinforcement that is heavier, more expensive, less readily available and more cumbersome to handle, in order that the abrasion-damaged tensile reinforcement meets the minimum design strength of the tensile reinforcement-to-wall connection. Extensive abrasion can lead to failure of the tensile reinforcement and collapse of the wall.
Accordingly, there is a need in the art for earth retaining walls with positive tensile reinforcement-to-retaining wall connections that minimize abrasion damage to the portion of the tensile reinforcement in direct contact with the bearing surfaces within the connection. It is to such that the present invention is directed.